I've worked at BK as a teenager, and we would run out of stuff on the weekly.
Forgot to check ice-cream inventory and didn't order ice-cream? "Sorry, our ice-cream machine is broken!"
Cleaning out the soda machines is a pain in the buttocks? "Sorry, the machine to the left is broken, but you can use the one to the right!"
Ketchup is a pain to fill up? "Sorry, the pump is broken, here, have some packets instead!"
No one thought of slicing tomatoes? "We ran out of tomatoes, sir!"
The salad chopper is dirty and no one thought of cleaning it? Yup, you guessed it! "We ran out of salad, m'am!"
To run out of Whoppers is easy, it's a different sized bread and patty than the burgers, hence the name. It's also quite irresponsible, given that it's the most popular sandwhich in BK, but whatever!